The present invention is concerned with the design and structure of rotating centrifuge baskets of the type used in industrial processes for the separation of solids and liquids.
When rotated, the shells of centrifuge baskets are subjected to circumferential or hoop stresses induced by the mass of the basket material (the self stress) and additional hoop stresses induced by the material in the basket being processed (the applied stress), the basket shell being subjected to a total hoop stress that is the sum of these two stresses. In addition, axial forces on the ends of the basket, induced by the material being processed, produce axial and bending stresses which, although less than the total hoop stress, are substantial if the material being processed is in the fluid state. In the present state of the art, baskets made for industrial centrifuges are constructed in steel, with strengthening rings of steel or of fibre-reinforced plastics (see for example GB 1554412) fitted on the outside to withstand the total hoop stress if the shell alone cannot support these stresses. The basket shell is perforated to allow the flow of liquid from the material being processed, the solids remaining in the basket to be discharged when the separation is complete.
Centrifuges are often required to discharge the separated solids at low speed (typically 50 rpm) having accelerated the material supplied to a spin speed (typically 1500 rpm) to perform the solid liquid separation - repeating this process cyclically and frequently (typically 25 times per hour). The energy demand to accelerate and decelerate the basket loaded with material is proportional to the total inertia of the loaded basket - that is the inertia of the mass of the basket plus the inertia of the material contained therein.
One disadvantage of the present state of the art for industrial centrifuges is the large inertia of the basket itself (typically 50-60% of the total inertia) giving a low "payload" (defined as: the inertia of the material being processed+total inertia) and correspondingly high energy consumption.
A second disadvantage is that the perforations in the shell result in local stress concentrations in the steel around each perforation in excess of the mean total hoop stress applied to the basket, together with a reduction in the cross sectional area of the shell available to support the total hoop stress.
A third disadvantage is that steel, being an isotropic material, is not fully utilised, as the stresses induced by the axial forces are less than the hoop stresses.
It is an object of the present invention to overcome, or at least to mitigate, these disadvantages of the prior art devices.